The present invention relates to the general class of perfluorinated compounds known as perfluoropolyethers and to their corresponding intermediates, which are fluoroalkyl ethers of polyhydric alcohols.
Perfluoropolyethers possess excellent chemical and thermal stability which ensures a wide field of application for these compounds as heat transfer media, sealing liquids, lubricants under extreme chemical conditions, additives for oils and greases, turbine propellents and hydraulic liquids. They exhibit low dielectric constants, high breakdown voltages and low loss factors in alternating fields which makes them particularly suited for applications in the electrical area. In the electronics industry, for example, perfluoropolyethers are particularly useful in vapor phase soldering or as convection cooling liquids in transformers or similar devices. Their excellent dissolving power for oxygen and carbon dioxide enables them to be used as oxygen conveyers in heart-lung machines and also directly as blood substitutes in living organisms. These products also find applications in many spheres of nuclear and chemical engineering. Because of their outstanding chemical resistance, they are superior to the polypropylene oxide fluids which hitherto dominated these application fields, especially at temperatures above 200.degree. C.
Currently available vapor phase soldering fluids can be relatively expensive to manufacture, and they may release toxic vapors at their decomposition temperatures. In addition, some have a high solubility in soldering rosin which requires expensive reclamation and reduces fluid life. The compounds of this invention are generally superior in one or more of these respects.
Compositions disclosed in the art which most closely resemble the compounds of this invention are found in U.S. Pat. No. 3,692,348 and its British counterpart, GB 1,450,467. These two patents describe perfluoroethyl and perfluoropropyl ethers having the following formula: ##STR1## Perfluoropentaerythritol tetraethyl ether and perfluoropentaerythritol tetrapropyl ether are examples of such compounds.
Both patents describe the synthesis of aliphatic and cyclic perfluoro-alkyl ethers in high yields in which tetrafluoroethylene or hexafluoropropene adducts of aliphatic or cyclic alcohols are subjected to electrofluorination.